Rheostat.



C. W. DUNHAM.

RHEOSTAT.

APPLiCATIQN FILED FEB. I? 191? Patented May 8, 191

FIG.2

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it... vlllIll a INVENTOR WITNESSES CHARLES w. nnitnnm orl rtnenwocnnononsn, PENNSYLVANIA, ASSIGNOR TO THE UNION SWITCH i.

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Be it known that LCrmnnns W. DUN- HAM, a citizen or" the United States,residin at Edgewcod Borough, in the county or Alleghengiand State ofPennsylvania, have invented 'crtirinnew and useful Improvements in Bhelstats, of which the following is'a specification'l s,

-This invention relates to rheostats.

One featureftof this invention resides in the provision, of a1 rheostatincluding a biased bridging contact member of such a character that whentraversed by current,

the biasing means for the membeii will lie,

unaffected by such current, there y insult ing the proper functioning ofthe biasing means. e

I will now describe one form of rheostat embodying my invention andwill. then point out the. novel features thereof in claims.

In the drawings, Figure 1 is a view showing in elevation and partly insection one form of rheostat embodying my invention. Fig. 2 is a topplan view of the rheostat shown in Fig. 1; Fig. 3 is a view showing n lK; Specification of Letters Patent.

in side elevation one of the arms .of the T bridging contact membershown in the pre ceding figures. Fig. 4 IS a top plan view of the armshown in Fig. 3. F1 r. 5 is a-detall perspective view of the sleeve ownin Figs. 1 and 2. Fig. 6 is a lragmentary v; ew sh'ov ving in verticalsection the inanncrin which the sleeve and the contactarms are asso:ciated with the operating screw.

Similar referel'ice characters refer to similar parts in each of theseveral views.

Referring to the drawin s indetail, the rheostat in the form here how'ncomprises a metallic base 10 having a gdepending sup. porting flange 11for maintaining the base elevated. Secured upon the base 16 by means ofscrews 12, 12, are a pair of vertically disposed porcelain spools 13,13, such screws being locked by means of a bar L.

These spools, as shown, are spaced apart and are of the same diameterand length. oiled 14m adapted to be connected to the 'terinl-y abouttheperiphery of each of the spools 13, 13 is a continuous resistanceunit 14, which, as here shown, is in the form of a elix. I p The upperends of the resistance units it,

nals of an external circuit by means of angle f plates 15, 55, securedin recessed portions of IGNAL COMZANY, 01* SWISSVALE, PENNSYLVANEA, ACQRIORA- niinos i-n'r.

Patented May 8, 1917.

Application filed February 17, 19 1 7. Serial No. 149,232.

the spools 13, 13. The vertical-portion of each plate 15' is providedwith a clamping porcelain bearing 20 fo'rmedin the base, 10,.

The upper end of, the operating "screw lil extends through a-pair oflocking bars 21, and 21 which span the) up ,er ends of the spools, asshown. lTheselocking bars. are

designed to removably'secure the operating screw in vertical positionbetween spools 13 and as here shown are clampedtogether in superimposedrelation upon the spools by means 0; screws 22, 22.

The bars 21, 21*? are formed at their medial portions with reverselytapered openings 23, 23* for receiving the operating screw 19. Theoperating screw is not provided with threads at the point at which itintersects the locking bars to permit free rotation of the screw. withinthe bars. The operating screw is, however, locked against longitudinalmovement by means of the locking bars. With the locking bars andoperating screw in thew-positions shown in Fig. 1, the) openings 23, 23?have their small ends registering with each other, the wallsot suchopenings engaging the unthreeded portions of the operating screw wherebyremoval of the ,operating screw. will, he. prevented. Nhe'n it isdesired to-remove the-operating screw, the screws 22 are first removed,then the locking bars are moved toward each other in oppositedirections, thereby-causing the largerends of the openings 23 and 23 toregister with each; other.. As the larger ends of the openings are of agreater width than the diameter of the operating screw, it is obviousthat the operating screw may'now be removed, I

The operating screw is adapted to be manually rotated in eitherdirection by means of a handle 24: to impart rectilinear movements to abridging eontact nember d signated generally atC. This bridging contactmember 'isdesigncd to electrically connect the resistance units 14:, iat any point within'their lengths to vary the resistance of an externalcircuit as is well thereof co-acting with the threads of the operatingscrew to move vertically upon the operating screw when the latter isrotated. The opposite 'ends of the sleeve S are formed with annularflanges25 and respectively between which is mounted the ridging contactmember, as will be hereinafter described.

The bridging contact member 0 comprises in this instance a. pair of armsA and A formed of electro-conducting material of low resistivity forelectrically connecting the resistance units 14, '14, and a pair ofbiasing members B and Bformed of electro-conductive material ofrelatively high resitivity for forcing the arms into engagement withboth of the resistance units. The arms A and A as shown in Figs. 1 and2, are arranged in superimposed relation upon the sleeve S between theflanges 25 and 26 and are mounted for swinging movement thereon. Thesearms are of identical construction and as shown in Fig 3and 4 each armcomprises a single length of material recessed at the medial portionthereof as at 27, to receive the sleeve S. The opposite ends of each armare offset in the same direction as best illustrated in'Fig. 3 and areprovided with reversely disposed contact tips 28, 28.

' When the arms A- and A are assembled upon the sleeve .8 they arereversely disposed to cause the contact-tips 28 to horizontal lane.

The biasing members B and B as here shown are in the form of coiledexpansiblc springs, each spring being interposed be tween adjacentcontact tips 28 of the arms to force the contact tips into engagementwith the resistance units 14, 14. Lugs 29 are formed on the contact tips28 for engaging lie in the same and holding the springs between thearms.

As clearly shown in Fig. 2 the opposite ends of the arms are biased in opositedirections 'ber C will be. shunted to cause the contact tips oeach arm to engage both of the resistance units thereby forming twoconducting paths of low resistahce for the passage of current betweenthe resistance units. As the springs B and B have a relatively highresistance as compared with the arms A and A, it is'o'bvious thatcurrent when traversin the bridging memt i'om the springs, the armsconducting the current from one resist ance unit to the other andthereby preventing the current from heating the springs to destroy theirresiliency.

By virtue of 'this construction and arrangement it will be evident thatthe current traversing the bridging contact member C will be i effectiveto destroy the resiliency of the bi 0g means, thus the properfunctioning of ie bi no' means maintained.

Althoug .r l snown and described only one fornfoi. rhea: at mnliod vingmy invention, it is to be understood that various changes andmodifications may be made without departing from the spirit and scope ofthe upper {ed claims.

Having thus described my invention, what I claim is: 1. A rheosta't comrisin a iair of resistu b l 0 ance units, a movable bridge connectingsaid units and comprising a pair of superimposed intersecting arms, andbiasing means interposed between the endsof the arms for retaining theil'mS in contact with said units, said arms biasing means bein formed ofconducting material of low and liigh electrical resistance respectively.

2. A rheostat comprising a pair of resistance units, a pair of movableintersecting arms, aranged tangentially with respect to said units, andbiasing means interposed between said arms for maintaining the relativepositions of the arms and for retaining the arms in contact with saidunits.

3. A rheostat comprising a pair of resistance units, if movable bridge.connectin said nuts and comprising a pair of crossed arms biased toengage said units, said arms being formed of conducting material, andmeans for moving said bridge over said units.

4. A rheostat comprising a. pair of resistance units, a movable bridgeconnecting said units and comprising movable members, and biasing meansof high electrical resistance for retaining said members in contact withsaid units, said members being formed of conducting material of bycurrent traversing shunted from said biasing means.

5. A rheostat comprisng a pair of resistance units, bridging arms forelectrically connecting said'units, said arms being movablewithrela-tion to said units and to each other, and biasing means forretaining said arms in contact with said units, said biasin means havinga higher resistance than said arms.

6.. A rheostat comprising a pairof resistance units, crossed armselectrically connecting said units, said arms being movable withrelation to said units and to each other, and coiled springs arrangedbetween the ends of the arms for biasing said arms into engagement withsaid, units.

7. A rheostat comprising a pair of resistance units, crossed armsarranged between said units and electrically connecting the same,biasing means for expanding the arms said. bridge Will be low resistancewherearms, and screw threaded means for simultaneously moving said armsover said units.

8. A rheostat comprising a pair of resistance units, a screw-threadedmember rota- 5 tably mouneed between said units, a sleeve threadedlyengaging said member, crossed conducting arms carried by said sleeve,and biasing means interposed between the opposite ends of said, arms :0arms into engage. ent with said units.

9. A. rheostat cei'nprising a pair of resistfon expanding said anceunits, crossed arms electrically connecting said units and movablethereover, and a spring for biasing said arms into engagement with saidunits, said spring being of a 15 hi her electrical resistance than saidarms. in testimony whereof I aflix my signature in presence of twoWitnesses.

CHARLES W. DUNHAM. Witnesses:

A. HERMAN WEGNER, R. Gnonen RUDMAN.

